1. Field of the Invention
The present invention generally relates to liquid withdrawal from a container. More particularly, the present invention relates to an apparatus that provides for withdrawal of the liquid contents from a closed container, independent of the spatial orientation thereof. The apparatus is useful in a self contained breathing apparatus (SCBA) type respirator for withdrawal of a liquefied breathable gas mixture from the container. However, in a broad sense, the present apparatus is useful for withdrawal of any liquid from a closed container by the pressure differential communicated between the inside of the container and a removal means located outside the container through a flexible conduit.
One preferred embodiment of the liquid withdrawal apparatus of the present invention includes a flexible conduit disposed inside a container and in fluid flow communication with an external heat exchanger. The heat exchanger serves to input heat energy from the ambient atmosphere to the withdrawn liquid to thereby provide a breathable gas mixture. The upstream end of the flexible conduit is provided with a weighted pick-up means that is either submerged in the liquid, or rests on or slightly submerged below the surface of the liquid to ensure only liquid withdrawal, independent of the spatial orientation of the container. Preferably, the pick-up means comprises a wicking material that draws the liquid into the interior thereof to further ensure contact of the liquid with the upstream open end of the conduit means. The flexible conduit then transmits through a pressure barrier at the container outlet to communicate with the heat exchanger. The pressure barrier seals around the flexible conduit to ensure that there is little to no communication of pressure between the inside of the container and the heat exchanger, other than the fluid flow communication path provided by the conduit itself. A pressure differential between the inside of the container and the external heat exchanger, normally brought about by an inhalation event of the user, provides the motive force for withdrawing the liquid contents from the container through the flexible conduit. Pressure inside the container is maintained through vaporization of the liquid contents which is saturated to some pressure, P, of about 100 psig, for example.
2. Prior Art
Various devices are known in the prior art for liquid withdrawal from a container associated with a breathing apparatus. German Patent No. 414107 relates to a respirator for liquid gases comprising a liquid gas receptacle having a pressure-compensating line and siphon line that are in large part non-rigid, flexible tubes. In one embodiment, the lowest end of the pressure-compensating line is mounted to a float so that at any position of the device, the inner orifice of the pressure-compensating line remains in the evaporation space while the siphon line is mounted to a weight so that the inner orifice thereof remains constantly immersed in the liquid. In another embodiment, both the pressure-compensating line and the siphon line are carried by the float in such a way that their orifices are in the evaporation space and immersed in the liquid, respectively. Other than being described as flexible, the material of construction of the pressure-compensating line and the siphon line in both embodiments is not further described. Further, the weight is not described as including a wicking material to ensure contact of the siphon line with the liquid gas at all times, for example when the liquid contents are nearly depleted.
U.S. Pat. No. 3,572,048 to Murphy describes an omnipositional cryogenic underwater breathing apparatus comprising a reservoir tank having two weighted liquid air pick-up tubes disposed transverse through the length of the tank. The pick-up tubes each are in turn connected to coiled tube sections which have spring like properties that permit the weighted ends of the pick-up tubes to fully move about the cross-section of the reservoir under the force of gravity. The coiled tube sections are not flexible and they do not permit movement of the pick-up tubes about the entire volume enclosed by the tank, as in the present invention.
U.S. Pat. No. 3,318,307 to Nicastro describes a breathing pack for converting liquid air or liquid oxygen into a breathable gas. This device includes a weighted liquid withdrawal tube extending laterally outwardly from a lower swivel. The lower swivel is connected by a pivot tube to an upper swivel which in turn has a gas pressurizing tube extending laterally outwardly therefrom, but in an opposite direction with respect to the liquid withdrawal tube. The weighted liquid withdrawal tube ensures that the liquid contents are fed to a heat exchanger to vaporize the liquid. However, the liquid withdrawal tube is not flexible and it would not be in contact with the liquid contents in all intended orientations of use of the container, for example, if the container was positioned upside down.
In the prior art apparatuses, the various withdrawal structures do not ensure liquid removal throughout the entire volume of the container particularly when the liquid quantity is low. The weighted pick-up head of the present invention is an improvement over the prior art in that the liquid withdrawal conduit is flexible and its pick-up end is provided with a wicking material so that, the upstream open end of the conduit contacts the liquid, even when the quantity of liquid is nearly depleted. When the container is incorporated as part of a SCBA and the liquid contents are a liquefied, breathable gas mixture, the construction of the present liquid withdrawal apparatus ensured that even in low liquid quantity situations withdrawn liquid continues to flow to the endothermic heat exchanger, which transfers heat energy from the ambient atmosphere to the liquid to vaporize the liquid to a breathable gas. This could be extremely important for saving a user's life if that person was trapped and their breathable liquefied-gas supply was running low. Furthermore, the weighted pick-up head ensures that only the liquid contents are removed from the container, devoid of any of the gaseous head, to provide the breathable gas having concentrations of the various constituents at a similar relative content as they are in the liquid phase. In other words, vaporization of the liquid contents only occurs in the heat exchangers at a rate relative to consumption at the facepiece. In this manner, the oxygen content of the vaporized gas remains at a concentration level similar to that of the cryogenic liquid.
U.S. Pat. Nos. Re. 33,567 to Killip et al., 5,417,073 to James et al., 5,243,826 to Longsworth, 4,756,310 to Bitterly, 4,750,551 to Casey and 4,218,892 to Stephens describe various apparatus having wicking material for conducting a liquid. However, none of these patents contemplates the use of a wicking material provided at the pick-up end of a liquid withdrawal conduit to ensure contact of the liquid with the conduit, even when the liquid is nearly depleted.